The present invention relates to the art of amplifying video signals. The invention finds particular application in conjunction with fluoroscopic/radiographic medical imaging systems and will be described with particular reference thereto. However, it is to be appreciated that the invention will also find application in multi-rate scan video camera systems with remotely selectable dual bandwidth/gain video preamplifiers.
In an x-ray fluoroscopic/radiographic imaging system, a radiation source directs x-rays through a patient onto an input surface of an image intensifier tube. The image intensifier tube converts a relatively large area of x-rays into a relatively small brightened visual image which corresponds to the x-ray pattern emerging from the patient. The image from the image intensifier tube is converted to a video signal by a video camera.
In the fluoroscopic/radiographic imaging system, the video signals from the video camera can be used in a variety of manners. First, the video signals can be sent directly to a viewing monitor which produces an image. In another option, the video signals can be directed to a variety of display processing components including digital acquisition systems, video tape recorders, and video disc recorders. These components digitize, enhance, and store the video signals so that they may be played back on a monitor at a later time.
One feature of these multi-mode diagnostic imaging systems is the different parameters which must be accommodated in changing modes. For example, a standard fluoroscopy mode employs a 525 lines per screen image. Whereas a high resolution radiographic mode employs a 1049 lines per screen image. Numerous adjustments, such as brightness, must be made for visual compatibility as a function of which line rate is selected. In playing back the stored information, the aspect of the monitor produced image is typically changed from a 1:1 to a 4:3 aspect ratio. Depending upon the mode selection, various degrees of resolution are obtained. These differing parameters are accommodated by adjustments to the monitor to produce an acceptable video image. In the past, one manner to satisfy these varying requirements was to create a system containing multiple monitors, each being preset for the operation in accordance with the various combination of parameters necessary for each operating mode. The parent applications disclose a system that employs a single monitor with associated control circuitry capable of displaying images from the various operating modes.
One of the problems encountered when forcing a plurality of modes into a common display format, is that some modes have a more unfavorable signal to noise ratio in the display format. Specifically, in the medical field, the video camera tube is commonly operated in three modes; (1) an interlace mode with 60 frames per second, (2) a non-interlaced progressive mode operating at 30 frames per second, and (3) a non-interlaced progressive mode at 7.5 frames per second. The slower third mode normally has significantly more image deterioration than the first two modes.
The present invention contemplates a new and improved camera system and method which over comes the above referenced image deterioration problems and others.